The only thing I can think of is to use like Relation to tie these things together using a relation as
Slideshow Content and then a field tacked onto the relation as
You should be able to then have any number of content types -- relate them to your slideshow and define the ordering as needed that content.
To ease the generation of relating (linking) things these additional relation modules may help:
Small block that allows the user to add an appropriate relation from
an entity page to any other appropriate entities, with a generic
autocomplete for each endpoint, and relation fields.
Module allows to setup invisible widget to Relation Dummy Field. This
widget loads information (entity type and ID) about another entity
from arguments in the path and create relation between determined and
newly created entity.
For example, you can use path "node/add/story/node/22" to connect new
story content with node number 22.
This module provides a field widget for creating & editing relations.
The selection interface is based on views. Use exposed filters to
search for entities, & select items from the view output displayed as
a clickable drop down list.
So the idea is you have all your content on the backend -- related via a Relation and its field to grab it for a Views Slideshow later. Some of these modules attempt to make creating that (meta-)relation with your slideshow content easier.
You might be able to use like Arrange Fields or FieldGroup to make a tab for "slideshow properies" for each of your content types that shows the Relation info in the node edit form.